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The phenotypic relevance of allelic variation in the structure of the beta 2-adrenergic receptor (beta 2AR) expressed in lung cells is unknown. In particular, altered responsiveness of the beta 2AR expressed on airway smooth muscle, which are responsible for bronchodilation in the treatment of asthma, may be an important factor in the ultimate physiologic response to agonist. To approach this, we established primary cultures of human airway smooth muscle cells obtained at autopsy and developed a method to determine the beta 2AR genotype at the polymorphic loci of codons 16 and 27, using allele-specific polymerase chain reactions. Radioligand binding studies revealed that these cells expressed approximately 70 fmol/mg of receptor which was exclusively of the beta 2AR subtype. All cell lines obtained (n = 10) exhibited normal agonist binding and receptor-mediated activation of the adenylyl cyclase second messenger pathway. However, distinct differences were found in the response to long-term agonist exposure between the different beta 2AR genotypes. Cells expressing Arg at codon 16 (Arg16) traditionally referred to as wild-type, underwent 77.8 +/- 8.1% downregulations of beta 2AR following prolonged (24-h) exposure to the beta 2AR agonist isoproterenol (10 microM). In contrast, cells expressing Gly16 beta 2AR underwent enhanced agonist-promoted downregulation (95.6 +/- 1.7%, P < 0.05 versus Arg16), whereas cells expressing Glu27 beta 2AR were relatively resistant to such downregulation (29.5 +/- 12.7%, P < 0.01 versus Arg16). For cells expressing Glu27 beta 2AR, this difference resulted in a significant attenuation of agonist-promoted functional desensitization (33 +/- 7 versus 90 +/- 5% desensitization for Arg16, P < 0.001) following preincubation with 1 microM isoproterenol.(ABSTRACT TRUNCATED AT 250 WORDS)
Green et al. (Sat,) studied this question.